In the process of drawing with a computer, it is frequently necessary to set a graphic on a display unit to a desired position or direction by finely adjusting its current position, angle, or size respectively.
One known conventional graphic processor utilizes a rectangular frame for control encloses a graphic subject to transformation. The graphic is displayed on the screen by specifying the subject graphic with a mouse and by dragging the mouse. The rectangular frame has control points at its four corners and the center.
When the operator selects a control point and drags the mouse, the subject graphic A rotates around the control point with the rectangular frame. However, it is frequently impossible to place the subject graphic at the correct position in respect to other graphics because the rotational center cannot be specified at a desired position. Therefore, it is necessary to repeat the operation for movement and rotation many times. Moreover, it is inconvenient to sequentially perform graphic processing such as movement, enlargement, contraction, and rotation because they are of separate modes. In addition, to enlarge the subject graphic, it is necessary to repeat the operation for enlargement and movement until the subject graphic is brought to a proper size and position because the central axis for enlargement is restricted to the center of the rectangular frame and the central axis cannot arbitrarily be designated.
Another known type of graphic processor allows the operator to specify the rotational centers of the subject graphic and the frame. For example, the official gazette of Published Unexamined Patent Application No. 2-292677 discloses a graphic processor in which a reference point serving as the center of the graphic processing function can be selected from specific positions. Also, the official gazette of PUPA No. 1-318168 discloses a document processor in which the origin serving as the center of the enlargement, contraction, or rotation function can be set at an arbitrary position. For these conventional graphic processors, however, it is only possible to change the size of the subject graphic in the X- and Y-axis directions of the graphic together with the frame about the origin (reference point). Therefore, it is impossible to transform the subject graphic in the X- and Y-axis directions of an arbitrary angle (in respect to the frame).
If the subject graphic can be transformed in the X- and Y-axis directions of any angle (in respect to the frame), it is believed that a curve with higher degree of freedom can be generated. For example, there is a case in which a curve with a proper curvature should be drawn in any section of a subject graphic A with a French curve. If it is possible to combine the subject graphic A with another graphic B corresponding to the French curve and change only the curvature of the graphic B without changing the position of the intersection between both graphics, a curve with a proper curvature can be drawn as if it is drawn with the French curve. The conventional graphic processor cannot perform the graphic processing with higher degree of freedom like the above.